1. Field of the Invention
This invention broadly relates to a hand-held socket wrench used to tighten or loosen fasteners such as nuts, bolts and the like. More particularly, the invention relates to a socket wrench having an impact drive useful for freeing stubborn fasteners or for tightening fasteners to a relatively secure position.
2. Description of the Related Art
Socket wrenches have been long considered as highly useful tools for a variety of industrial, commercial and residential tasks. Socket wrenches typically include an elongated body having a handle at one end and a drive shank near the opposite end. The drive shank extends in a direction perpendicular to the length of the body and has an outer end section that is adapted to releasably fit into a matching hole in one end of a socket.
Sockets are available in a number of different metric and SAE sizes to fit various nuts, bolt heads and other fasteners having a hexagonal or square head. Sockets are also available with drive bits to fit Phillips, slotted or Torx head fasteners. Sockets and socket wrenches are considered economical to purchase and maintain because only one socket wrench is needed to drive any one of a number of differently-sized sockets.
Many socket wrenches include a ratchet mechanism that allows the user to advance the socket and hence the fastener in a certain rotational direction by repetitive, reciprocal motion of the handle along an arc of limited length. Ratchet drive socket wrenches are particularly useful in areas where clearance space next to the fastener is limited and the handle cannot be swung in a full, 360 degree arc. The ratchet drive is usually reversible so that the socket wrench can be used in either rotative direction as may be needed, for example, to tighten or loosen a threaded fastener.
Socket wrenches are also available with drive shanks of different cross-sectional sizes. Socket wrenches with smaller drive shanks are adapted to couple to smaller sockets for driving relatively small fasteners, while socket wrenches with larger drive shanks are adapted to couple to larger sockets for driving relatively large fasteners. Typical sizes of drive shanks include one-quarter inch square and three-eighths inch square for smaller sockets, and one-half inch square and three-quarter inch square for larger sockets.
In physics, "torque" is a force that produces or tends to produce a twisting or rotational motion. The amount of torque provided by a socket that is connected to a socket wrench is calculated by multiplying the force that the user exerts on the handle by the distance between the handle and the central, rotational axis of the drive shank of the socket wrench. Consequently, the torque provided by the socket to the fastener for any given amount of force exerted by the user on the handle can be varied by varying the distance between the handle and the drive shank.
The length of socket wrenches (i.e. the distance between the rotational axis of the drive shank and the handle) is usually chosen by the manufacturer to match the amount of torque that is expected to be needed to loosen or tighten the fasteners typically encountered during use. For example, socket wrenches with smaller drive shanks are usually coupled to smaller sockets for use with relatively small fasteners. Manufacturers often provide such socket wrenches with a body of relatively limited length so that when the user exerts a reasonable amount of force on the handle to tighten the fastener, the torque in most circumstances will not be sufficient to break the fastener.
Similarly, socket wrenches with larger drive shanks are often coupled to larger sockets for use with relatively large fasteners. Larger shank socket wrenches are normally equipped with a body having a relatively long length so that a sufficient amount of torque can be exerted on the fastener to securely tighten the fastener. In these wrenches, the distance between the handle and the rotational axis of the drive shank is sufficient to provide a satisfactory amount of torque to the socket without requiring the user to exert an undue amount of force on the handle.
Unfortunately, users of conventional socket wrenches are sometimes unable to exert a sufficient amount of force on the handle to loosen particular fasteners. For example, fasteners that have been over-tightened and fasteners that have oxidized or rusted are often difficult to loosen and remove. Rusted fasteners are often encountered when repairing automobiles, especially if the fastener is located on the underside of the automobile or in other areas where water and road salt are present. Lug nuts on older automobiles may be particularly difficult to remove. Additionally, fasteners used near a salt water environment such as those used in boats, automobiles and buildings near the ocean are highly susceptible to severe corrosion.
Other examples of fasteners that may be difficult to remove include threaded fasteners that have been coated with a thread locking compound, and fastening assemblies made of two dissimilar metals that, over time, have chemically reacted and bonded to each other. Aircraft locking fasteners, such as fasteners that include a nut having peened-over portions near the threaded bore, can also be difficult to remove.
Occasionally, attempts are made to remove stubborn fasteners by using a "breaker-bar" socket wrench having a body with a length longer than normal. The increased length of the body increases the torque applied to the fastener for a given amount of force applied to the handle by the user, and in some instances is sufficient to remove the fastener. Such socket wrenches often lack a ratchet mechanism and instead have a "T"-shaped head that is connected to the drive shank.
Unfortunately, breaker-bar socket wrenches are most often used in a manner by applying a gradually-applied force to the fastener, which may not be effective in some instances without undue effort. In addition, long breaker-bar socket wrenches cannot be used in locations where access is limited. The length of breaker-bar wrenches also sometimes facilitates slipping of the socket from the fastener, which may lead to injury to the user. Moreover, breaker-bar socket wrenches that lack a ratchet mechanism are often a nuisance to use once the fastener has been loosened, particularly in areas where there is insufficient clearance to swing the handle in a 360 degree arc. It is also somewhat time-consuming to remove the socket from the shorter socket wrench normally used and replace the shorter wrench with the longer, breaker-bar socket wrench.
Electric and air-powered impact wrenches are used by some mechanics to loosen stubborn fasteners. However, such powered wrenches are somewhat costly and cannot be used in locations where a source of power or compressed air is not available. Powered wrenches are sometimes considered too cumbersome and too powerful for use with smaller fasteners. Furthermore, if the mechanic is using a socket wrench for other fasteners, it is somewhat of a nuisance to put the socket wrench aside and retrieve the powered impact wrench each time that a stubborn fastener is encountered.